biology question #2991

the answer

Short answer: Sugar acts as a preservative by sucking the water out of bacteria and other potentially harmful agents that might contaminate food. It might seem strange, because you might be thinking that bacteria like sugar. They do. But it you put A LOT of sugar like the amount in jam or in canned preserves the bacteria get overwhelmed.

The name of the scientific principle involved is osmosis. Bacteria are single cell organisms and the outer cell wall lets water, salts and sugars go in and out in a controlled way. Most of the cells in your body are the same. In a healthy system, there is a nice balance between what is inside the cell and what is outside. That is: you have about the same amount of water and molecules outside as inside, but they are different molecules. We say the concentration is about the same. When you get a HUGE amount of sugar (or salt) outside the cell, it puts a kind of pressure on it. The sugar is WAY more concentrated outside than it is inside. The cell wants things to be the same inside and outside or else it feels out of balance. Having things the same is called equilibrium. If there is a ton of sugar outside, and not much inside, then there is this pressure either to get more sugar inside, or to get more water outside. The cell can't get any more sugar into it because there's no room, so instead it pushes out water to try to maintain a balance. This happens so much that the cell kind of puts out ALL its water, and so it sort of dries up and dies. You can preserve things in salt the same way. That's why you have salty pickles and salty meat salami, salt cod, etc.